1. Field of the Invention
This invention relates to electrical generators, and more particularly to generators having bearings for supporting the drive shaft and to a system for detecting the imminent failure of such bearings and the need for bearing replacement.
2. Description of the Prior Art
In electrical generators, such as those used to power the electrical systems of aircraft, the generator is connected to the main engine by a drive shaft. The rotor assembly is mounted on the shaft and rotates within the stator assembly. The shaft is supported for rotation in the generator housing using sealed bearing assemblies comprising grease lubricated ball bearings. In the course of normal generator operation, the bearings are subject to wear. Eventually, the bearings can wear sufficiently that bearing failure can occur, causing the generator to stop functioning. If the generator stops functioning, the aircraft electrical system may not operate.
In order to prevent bearing failure and to maintain proper operation of the generator, the bearings are usually replaced at predetermined service intervals. The bearing replacement intervals are determined based upon worst-case scenarios of bearing wear, and the bearings are scheduled for replacement before any reasonable possibility of bearing failure can occur. As a result, the bearings are usually replaced long before they are actually worn out, and generators are disassembled and serviced unnecessarily before there is any immediate need for bearing replacement. This results in unnecessary servicing, cost and equipment downtime.
In any event, this unnecessary servicing has still been preformed because there has been no means by which one could determine whether or not the bearings were close to actual failure, and preventive maintenance needed to be preformed because of damage to the generator, and possible loss of electrical power that would result if the bearings actually failed.